New Routes for Thermal Analysis and Calorimetry As Applied to Polymeric Systems

Over the last few decades there has been a strong decrease in the number of Thermal Analysis and Calorimetry (TA and C) ‘practitioners’ - scientists who know the in sand outs of TA and C and its (im)possibilities and are capable of initiating new developments. By contrast, an increasing number of TA and C ‘users’ are scarcely able to acquire in-depth knowledge of TA and C. It is therefore of great importance that national TA and C societies create the infrastructure for dedicated education. In addition, the feasibility of setting up one or more expertise centers per country, where ‘practitioners’ can do research,carry out contract research and give advice to users, needs to be investigated. Equally important, the TA and C community needs to address a number of challenges in the coming decade with the aim of controlling the ‘knowledge cycle’ in the field of polymers: to translate non-optimal properties into improved processing conditions or even a more suitable macromolecular architecture, in order to reduce the lead times for the development and optimization of materials. Although Thermal Analysis and Calorimetry can generally be considered to be ‘mature’, in specific subareas a large number of new developments take place. A few examples of these developments and of state-of-the-art TA and C are given:quantitative heat capacity measurements by means of DSC; (very) high pressure DSC;real-time morphological analysis and temperature-modulated X-ray analysis. In addition, anew form of TA and C is discussed: High Performance DSC (HPer DSC), which is also a high rate DSC and a high throughput DSC. This revised version was published online in July 2006 with corrections to the Cover Date.     

Decomposition of DSC curves of dairy products with Gaussian functions

Summary DSC measurements have wide application in the field of biochemical/biophysical research to look into the melting behaviour of muscle proteins in different intermediate states of ATP hydrolysis cycle as well as in the field to develop dairy products. It was a demand to develop a deconvolution program to evaluate and interpret the background of DSC scans such a way that the decomposition into a proper function has to be simple and quick. There should be possible to choose the proper parameters as well as to calculate the data of decomposing curves with the simultaneous graphic representation of them including the resultant DSC scan as the sum of decomposing functions. In most cases Gaussian function is used for this purpose. Our main field of interest is the food physics where e.g. the proliferation of different probiotic bacteria follows a lognormal distribution, its first derivative is a Gaussian one, for this reason we have chosen it. The main parts of this PC program are: -the process of fitting and calculation of Gaussian functions, a multiple step correction of these function (optimal fitting), graphic representation of all functions. An example is shown for its application how to analyse the melting of butter fat.     

Thermoanalytical methods in the study of inorganic thin films

Thermoanalytical (TA) methods are relatively seldom applied for assessing the physical and chemical proeprties of thin films, but they can be used in studies of composition, phase transitions and film—substrate interactions. In the present paper the possibilities of TA methods in thin film studies are reviewed. The thermoanalytical methods considered are the classical TG and DTA/DSC methods but some complementary methods will also be briefly mentioned. The main emphasis is given to true thin films. Details of sample preparation are also given. An important application of TA methods is characterization of precursors for the CVD growth of thin films, and this is also discussed.     

浅析氨基酸代谢在生物有机化学与化学生物学教学中的重要性

从氨基酸代谢的基本内容出发,分析并整理了其在生物化学教学中的意义与教学要点,其中富有的各种生物化学过程也充满了趣味性,对于本科生教学是良好的素材。在举例阐述其多样性、复杂性、趣味性与启发性的基础上,讨论生物化学教学中氨基酸代谢相关内容,是一种将前沿科学融入基础生物化学教育的新探索。     

A combined photoacoustic DSC for simultaneous temperature modulated measurements: does it really work?

Combination of two techniques, photoacoustic (PA) and differential scanning calorimetry (DSC), is a combination of quasi stationary thermodynamic DSC method and nonstationary dynamic PA method. Especially favorable and easy to realize is the combination with power compensated type of DSC. It has several advantages over the use of two techniques separately and allow to perform measurements simultaneously. The most obvious is simultaneous determination of thermodynamic properties such as specific heat, heat of transition and dynamic properties such as effusivity, thermal conductivity at the different phase transitions and complex specific heat at the glass transition. Unlike other temperature modulated techniques PA–DSC is especially suitable for studying polymer materials since their low thermal conductivity is an additional advantage. Conditions for simultaneous measurements are examined. It is proved that the combination of two techniques and necessary changes in construction do not essentially change adequate work of the instrument. A little disbalance of DSC operation due to the construction change can be corrected simply by recalibration. The procedures for testing and calibration for the proper operation of the combined PA–DSC are given together with some details of experimental methodology. Several measurements could serve as examples of widespread applicability of PA–DSC to study different types of phase transitions as well as time dependent processes such as glass transition.     

调制差示扫描量热法研究玻璃化转变温度

对比了DSC与MDSC试验技术的差别， 列举了MDSC的优点，MDSC不但可以给出普通DSC的所有信息，而且给出更多的普通DSC无法提供的信息。MDSC特别适合于复杂转变、弱的转变分析，可以寻找出隐藏在熔融及结晶过程中的玻璃化转变。MDSC对于试验条件的选择比较苛刻，在选择好基本的试验参数的前提下，还需要设置调制周期、调制振幅等参数。     

Thermal and dynamic behaviour of the actin monomer in case of different cations

Actin is one of the important elements of the striated muscle that transmits force from the myosin filaments and as a part of the cytoskeleton plays an important role in shape determination of cells. It is a known experience that removal of the divalent cation affects the dynamic behaviour of actin in both forms. Paramagnetic probes and electron paramagnetic resonance (EPR) spectroscopy provide direct technique by which the rotation and the orientation of specifically labelled proteins can be followed during biochemical manipulations. The spectroscopic measurements could be combined with DSC measurements that report domain stability and interactions and allow the calculation of the thermodynamic parameters during the melting process. Actin was spin-labelled with maleimide or fluoro-dinitro proxyl probe molecules which are bound to the Cys-374 or Lys-61 residues of the smaller domain. EPR spectroscopy spectra were recorded in monomer form in Ca- and EGTA-state as a function of temperature up to the melting point. Similarly, DSC measurements were performed and analyzed using the kinetic theory. The measurements showed that removal of the divalent cation from the globular actin induced significant local and global structural change both in the thermodynamic properties and the rotational mobility of actin detected by DSC and EPR. On the basis of the results derived by deconvolution of the DSC pattern we can suggest a non-interactive two-domain melting for the monomer actin after removing the divalent cations.     

DSC by the TGA/SDTA851e Considering Mass Changes

DSC measurements in open pans are often disturbed by mass losses such as sublimation during melting or release of water during chemical reactions. By simultaneous DSC and TG measurements the DSC signal can be corrected. For this purpose, a temperature dependent calibration function has to be determined by which the SDTA signal from the TGA/SDTA851^e measuring cell can be converted into a heat flow curve (DSC). By this procedure, accurate heat of melting can be determined despite ongoing sublimation in open pans. This method is illustrated with reference of the melting of anthracene. Additionally, condensation reactions were investigated and analyzed by DSC/TG even under ambient pressure, knowing the heat of evaporation. Using phenol formaldehyde resins the influence of the presence or the release of volatile reaction products on the reaction rate and kinetic parameters were studied. In general, the method can be used to correct DSC curves for thermal effects related to mass change. This revised version was published online in July 2006 with corrections to the Cover Date.     

甲壳素类液晶高分子的研究Ⅷ. N-邻苯二甲酰化壳聚糖/DMSO液晶溶液的热致相转变

合成了氮上完全取代的邻苯二甲酰化壳聚糖 (PhthCS) .用DSC研究了PhthCS DMSO液晶溶液的热致相转变 .偏光显微镜和DSC测定都表明临界浓度为 43wt% .在浓度高于 43wt%的溶液的DSC曲线中观察到了除了液晶 各向同性液体转变 (清亮点 )外还有一个明显的凝胶 溶胶转变 .凝胶 溶胶转变温度和转变焓均比文献报道的不规则取代的N 邻苯二甲酰化 O 乙酰化壳聚糖大得多 ,可见取代的规整性对凝胶 溶较转变有很大的影响 .根据DSC研究结果绘制了PhthCS DMSO体系的相图     

Fragility of supercooled liquids from differential scanning calorimetry traces: theory and experiment

Starting from the Debye model for frequency-dependent specific heat and the Vogel-Fulcher-Tammann (VFT) model for its relaxation time, an analytic expression is presented for the heat capacity versus temperature trace for differential scanning calorimetry (DSC) of glass transitions, suggesting a novel definition of the glass transition temperature based on a dimensionless criterion. An explicit expression is presented for the transition temperature as a function of the VFT parameters and the cooling rate, and for the slope as a function of fragility. Also a generalization of the results to non-VFT and non-Debye relaxation is given. Two unique ways are proposed to tackle the inverse problem, i.e., to extract the fragility from an experimental DSC trace. Good agreement is found between theoretically predicted DSC traces and experimental DSC traces for glycerol for different cooling rates.     

Measurement of heterogeneously catalyzed gas reactions by DSC

Gas reactions, catalyzed by solid catalysts, can be measured by DSC. In the experimental set-up an open sample pan with catalyst (powder or pellet) is placed on the sample side of the DSC sensor. The reactive gas mixture flows through the cell and reacts on the catalyst surface. The heat effect, caused by this reaction, results into a DSC signal.The calibration procedure is described for quantitative evaluation of the DSC measurements. For illustration four different reaction systems are discussed.     

Curing of alkyds based on semi-drying oils with melamine resin

An alkyd/melamine resin mixtures are mainly used in industrial baking enamels. The aim of this work was to study the curing behaviour of alkyds based on dehydrated castor oil and soybean oil with melamine resin by differential scanning calorimetry (DSC). The kinetic parameters obtained by the transformation of dynamic DSC results into isothermal data through Ozawa kinetic model are in good agreement with those determined by the isothermal DSC experiments. The apparent degree of curing, determined by DSC measurements and sol/gel method, has a pronounced effect on the hardness of the resultant coating film.     

Management and querying of morphological,physiological, biochemical and chromatographic data describing microbial strains

An interactive information system, MICRO-IS, is described. It comprises morphological, physiological, biochemical, and Chromatographic data describing microbial strains. A wide variety of retrieval, management, and editing functions can be invoked with easy-to-learn, user-oriented commands.     

聚甲基丙烯酸胆甾醇酯共聚物的合成、结构与性能研究 Ⅳ.PMACE的相态转变及光学性质

Finkelmann和等人对侧链胆甾型高分子液晶的研究表明,将具有液晶功能的低分子基团,经过一个软段连接到柔性高分子主链上的梳型高分子在一定的温度下可以形成液晶态,调节侧链高分子液晶的分子结构、软段长度,可以改变其相态转变温度及微区形态。前已报导具有不同侧链结构的聚甲基丙烯酸胆甾醇酯共聚物的合成、相态转变及光学性质,本文通过对聚甲基丙烯酸胆甾醇乙烯酯共聚物(PMACE)的液晶态及结晶态的微细结构及相态转变与胆甾侧链含量关系的研究,给出了液晶态的形成条件及结构特征。     

Biochemical reaction engineering for redox reactions

Redox reactions are still a challenge for biochemical engineers. A personal view for the development of this field is given. Cofactor regeneration was an obstacle for quite some time. The first technical breakthrough was achieved with the system formate/formate dehydrogenase for the regeneration of NADH2. In cases where the same enzyme could be used for chiral reduction as well as for cofactor regeneration, isopropanol as a hydrogen source proved to be beneficial. The coproduct (acetone) can be removed by pervaporation. Whole-cell reductions (often yeast reductions) can also be used. By proper biochemical reaction engineering, it is possible to apply these systems in a continuous way. By cloning a formate dehydrogenase and an oxidoreductase "designer bug" can be obtained where formate is used instead of glucose as the hydrogen source. Complex sequences of redox reactions can be established by pathway engineering with a focus on gene overexpression or with a focus on establishing non-natural pathways. The success of pathway engineering can be controlled by measuring cytosolic metabolite concentrations. The optimal exploitation of such systems calls for the integrated cooperation of classical and molecular biochemical engineering.     

Nanoliter-scale reactor arrays for biochemical sensing

A general approach is described for array-based biochemical sensing that uses contact-free dispersal of compounds into addressable microfabricated reactors. The arrays are composed of 1 to 100 nL volume open reactors that have been microfabricated on quartz substrates using lithography. The open architecture of these reactors allows them to be addressed in parallel or individually with an ink-jet arrayer that is capable of distributing 0.004 to 1 nL volumes of reagents. A seven-step biochemical assay has been conducted on a small array of reactors to demonstrate how they can be integrated with an ink-jet arrayer and optical detector. This nanoreactor assay format appears to overcome several limitations that chip-based microarray technology currently imposes on protein assays: the arrays can be created in a manner that does not expose the biochemical reagents to osmotic stress, independent reactions can be conducted in individual reactors, and the conditions in all of the reactors (e.g., concentration and pH) can be rapidly scanned. We believe that these nanoreactor arrays will be useful for biochemical sensing that involves delicate proteins and protein assemblies.     

Applicability of Kissinger model in nonisothermal crystallization assessed using a computer simulation method

The Kissinger method is one of the most popular approaches for determining kinetic parameters from the nonisothermal processes. The applicability of the Kissinger model in describing the nonisothermal crystallization was verified using the data of the simulated experiments with the given crystallization mechanism. The results show that the data of the Monte Carlo experiments for nonisothermal crystallization can be used to evaluate the nonisothermal crystallization model. The Kissinger model can be used to estimate the parameter of the activation energy of the nonisothermal crystallization from the DSC curves with the different heating rates, but unsuitable to obtain the parameter from the DSC curves with the different cooling rates.     

A simple method for determining activation energies of organic reactions from DSC curves

An approximate formula for a rapid and simple estimation of activation energies from DSC curves is given and applied to various homogeneous reactions. The results obtained are compared with the approximate values of the Duswalt method and with the results by the mathematically more demanding method of Borchardt and Daniels (additional application of multiple linear regression). In this connection the efficiency of the new approximation method is demonstrated.     

Temperature Modulated DSC (TMDSC) Applications and Limits of Phase Information, cp Determination and Effect Separation

The ADSC (Alternating DSC [1]) technique superimposes upon the conventional constant heating rate a periodically varying modulation [2–8]. The modulation creates high instantaneous heating rates which increases sensitivity. The low underlying constant heating rate is used to get better resolution. With ADSC it is possible to separate overlapping thermal effects without loss of sensitivity and to determine heat capacities under quasi-isothermal conditions. It has been reported that there are also some limitations for the use of the modulation techniques, i.e. that the accuracy of c_p determination is reduced at higher modulation frequencies due also to thermal diffusivity within the sample itself [9, 10]. In this contribution, the limitations given by the measuring system itself will be discussed. A key value is the limit frequency of the sensor arrangement. In the Mettler Toledo DSC821^c this frequency is approximately 1/3 Hz. From these findings the following recommendations amongst others can be given: for light mass crucibles, 30 s periods are reasonable with amplitudes not exceeding the heating/cooling rates possible. A blank and a calibration measurement will eliminate cell asymmetry and will enhance the accuracy of c_p measurements even at higher modulation frequencies. This revised version was published online in August 2006 with corrections to the Cover Date.